Despite advances in vetreous surgery, the procedure of membrane removal remains a hazardous untertaking, even for the most skilled surgeon. One proposed method of facilitating membranectomy is to digest the scarred tissue with extremely purified bacterial collegenase, incorporating the injection and incubation of the enzyme as part of the vitrectomy procedure. Recent data concerning the presence of collagen in multiple vitreous and preretinal membrans makes investigating the applications of collagenase even more feasible. Our laboratory has shown that there is no morphological or electrophysilogical damage to the rabbit retina when purified collagenase is injected into the vitreous for thirty minutes, followed by vitrectomy. We have also shown by electron microscopy that collegenase causes substantial digestion of intravitreal scars in rabbits. The resaons for the lack of toxicity are (1) that the enzyme is removed from the eye as port of the irrigation/aspiration procedure in vitrectomy; (2) the collagenase preferentially digests the Type I cicatricial collagen produced by fibroblasts rather than the Type IV basement membrane collagen present in the inner limiting membrane. The purposes of this project are first to determine by measurements of aspiration pressure during vitrectomy whether collagenase is indeed effective in facilitating intravitreal scar removal in rabbits. This is a necessary study to perform before collagenase can be considered for human intravitreal use. Physical measurements will be performed with and without enzyme, using a micropressure transducer inserted into the aspiration tubing of the vitrectomy instrument. In the second part of the study, we will perform more detailed toxicity studies. The electron microscope will be used to assess immediate retinal toxicity when collagenase is injected into rabbits which have undergone retinal photocoagulation and cryoretinopexy. Long-term toxicity studies will also be performed, using electroretinography, clinical evaluation, and electron microscopy.